Weight painting is causing weird extrusions
It looks like a Mixamo action... i.e. Y up. Their weight paint to start with is not good. You can not this also in their screen animations - the moves are problematic, hands cross the leg etc'
When you import it into Blender, it's even worse.
You can either try to re-target with a paid addon (eg:AutoProRig). But you would still need to have a solid blender rig to be the target.
Then, their meshes are triangulated and not with quads like blender which makes the weight painting task more tedious and less intuitive.
But even with a very good rig and proper mesh it is nearly impossible to use this rig as is. You need additional bones or else the meshes will cross each other.
I would suggest to try it on a simpler object before.